Liver Function Test Results Explained: ALT, AST, GGT and More
Last updated: August 2026
A liver function test is a panel of blood markers, and only some of them measure function at all. ALT, AST, ALP and GGT are damage and blockage markers that leak from liver or bile duct cells. Albumin, bilirubin and clotting time are the ones that reflect how well the liver is actually working. A mildly raised ALT is common, and in the UK the single likeliest explanation is fat in the liver rather than alcohol. One abnormal result is a prompt to investigate, not a diagnosis.
Key takeaways
- ALT is the most liver-specific marker on the standard panel. AST also comes from muscle, so it rises after hard exercise.
- A raised GGT on its own is very common and is not proof of alcohol use, though alcohol is one cause.
- Albumin, bilirubin and clotting are the true function tests. Abnormalities there are more significant than a mildly raised enzyme.
- The commonest cause of a mildly raised ALT in the UK is fat in the liver, now called MASLD, which is driven by weight and insulin resistance.
- Nothing you buy detoxes a liver. The things that measurably change liver blood tests are weight, alcohol, activity and reviewing medicines.
What does the liver actually do?
The liver runs several hundred processes, but five of them explain almost every abnormal blood test. It makes proteins including albumin and clotting factors, it stores and releases glucose, it processes fats and cholesterol, it produces bile so fat can be absorbed, and it chemically modifies drugs, hormones and waste products so they can leave the body in bile or urine.
That last job is what wellness content calls detoxification, and it is worth being precise about it, because the real version is more interesting than the marketing version. The liver runs substances through phase one reactions, which alter the molecule, and phase two reactions, which attach something water-soluble so it can be excreted. It is continuous, automatic, and not something a juice or a supplement switches on. When it genuinely fails, as in advanced cirrhosis, the result is a medical emergency such as confusion from ammonia build-up, not vague tiredness.
What do ALT, AST, ALP, GGT, bilirubin and albumin mean?
Each marker tells you about a different compartment: enzymes inside liver cells, enzymes lining the bile ducts, the pigment the liver clears, and the proteins it manufactures. Reading them as a pattern rather than one at a time is what turns a confusing printout into useful information.
| Marker | What it is | What a high result suggests | Common non-liver reasons |
|---|---|---|---|
| ALT | Enzyme inside liver cells, the most liver-specific one | Liver cell injury, most often fat in the liver | Rarely, muscle injury |
| AST | Similar enzyme, also present in muscle and heart | Liver injury, and an AST above ALT can suggest alcohol | Hard exercise, muscle damage, statin-related muscle effects |
| ALP | Enzyme from bile ducts and from bone | Blocked or inflamed bile ducts | Bone growth in teenagers, pregnancy, bone disease |
| GGT | Bile duct enzyme, very sensitive but not specific | Used to confirm a raised ALP is coming from the liver | Alcohol, many medicines, fatty liver, obesity |
| Bilirubin | Pigment from broken-down red blood cells | Jaundice, obstruction, or impaired processing | Gilbert's syndrome, a harmless inherited variation, and fasting |
| Albumin | Main protein the liver makes | A low level can indicate long-standing liver disease | Malnutrition, inflammation, kidney protein loss |
| Prothrombin time or INR | How quickly blood clots, using liver-made factors | A prolonged time suggests significant loss of function | Warfarin, vitamin K deficiency |
Why the name is misleading: ALT, AST, ALP and GGT do not measure function. They measure leakage. Someone can have significant cirrhosis with near-normal enzymes, and someone can have a markedly raised ALT with a liver that is working perfectly well. That is why doctors look at albumin, bilirubin, platelet count and clotting alongside them, and why one number on its own answers very little.
What does a raised ALT usually mean?
In the UK the commonest explanation for a mildly raised ALT found on a routine blood test is metabolic dysfunction-associated steatotic liver disease, or MASLD, which is the condition renamed from non-alcoholic fatty liver disease in 2023. It is driven by excess weight, insulin resistance and high triglycerides rather than by alcohol, and it is now very common.
The other causes worth knowing, in roughly the order a GP will think about them:
- Alcohol. Classically raises GGT and produces an AST higher than ALT, though the pattern is not reliable enough to diagnose or exclude it.
- Medicines and supplements. Including some antibiotics, anti-epileptics, high-dose paracetamol, and a long list of herbal and bodybuilding products.
- Viral hepatitis. Hepatitis B and C are treatable and often silent for years, which is why testing is standard when enzymes are up.
- Autoimmune and inherited conditions. Autoimmune hepatitis, haemochromatosis and, in younger people, Wilson disease.
- Coeliac and thyroid disease. Both can raise liver enzymes and both are easy to test for.
If yours came back raised, our detailed guides on fatty liver symptoms and what they really indicate and on what actually reduces liver fat pick the story up from there.
Do statins damage the liver?
Statins can cause a mild, usually transient rise in ALT in a small minority of people, and clinically significant liver injury from them is rare. Current UK practice does not require routine repeat liver monitoring indefinitely, and a mildly raised ALT is not in itself a reason to stop. Deciding to stop a statin without medical advice trades a rare and reversible blood test change for a real increase in cardiovascular risk.
Two further points that contradict the article this page replaced:
- Statins are generally considered safe in chronic liver disease, including in fatty liver, where they are often continued precisely because cardiovascular disease, not liver failure, is the leading cause of death in that group.
- The muscle symptoms people associate with statins are separate from liver effects. Muscle aches with a very high creatine kinase need urgent review, but that is a muscle issue that can nudge AST up, not liver damage.
If you are worried about your statin, the right move is a medication review, where the dose can be adjusted or the drug switched. That conversation is free and takes ten minutes.
Do milk thistle, dandelion and liver detox supplements work?
There is no good evidence that milk thistle, dandelion root or any liver detox formulation improves liver blood tests or liver outcomes in people. Trials of silymarin, the milk thistle extract, have been mostly small and inconsistent, and larger studies have not shown a meaningful benefit.
More importantly, herbal and dietary supplements are now a recognised cause of drug-induced liver injury, and they are one of the things a hepatologist asks about first when someone presents with unexplained abnormal liver tests. Green tea extract in high doses, turmeric and curcumin extracts, garcinia, and several bodybuilding products have all been implicated in case reports. In the UK you can report a suspected reaction through the MHRA Yellow Card scheme.
The honest bottom line on supplements: the paradox of taking something for your liver is that supplements are one of the more common reasons liver enzymes go up in the first place. If your results are abnormal, bring every bottle in your cupboard to the appointment, including protein powders and pre-workouts, rather than adding another one.
What genuinely improves liver blood tests?
Four things have real evidence behind them, and none of them is bought in a health food shop. Weight loss is the strongest lever by a distance: losing around 5 percent of body weight reduces liver fat, and around 10 percent can improve inflammation and scarring in MASLD.
| Action | What the evidence supports | Realistic timeframe |
|---|---|---|
| Gradual weight loss | 5 percent reduces liver fat, 10 percent can improve inflammation | 3 to 12 months |
| Reducing alcohol | GGT often falls within weeks of cutting down | 4 to 8 weeks |
| Regular activity | Reduces liver fat even without weight change | 8 to 12 weeks |
| Reviewing medicines and supplements | Removes a treatable cause of raised enzymes | Weeks, once the culprit stops |
| Coffee | Consistently associated with lower liver enzymes and less fibrosis in observational studies, though association is not proof | Long term, and not a treatment |
Two things worth adding that are not on the table: hepatitis A and B vaccination is recommended for people with chronic liver disease, and keeping paracetamol within the stated dose matters more than people assume, particularly alongside regular alcohol.
See a GP promptly, and urgently if severe
- Yellowing of the eyes or skin, dark urine, or pale stools
- Swelling of the abdomen or ankles
- Vomiting blood, or black tarry stools, which is an emergency
- Confusion, drowsiness or personality change in someone with known liver disease
- An abnormal liver result that has not been followed up, or is rising on a repeat test
Does liver health affect your hair?
Not through toxins, and we should say so clearly since the earlier version of this article claimed otherwise. There are two real connections and both run through nutrition and metabolism rather than detoxification.
The first is malabsorption. If bile flow is genuinely impaired, fat-soluble vitamins A, D, E and K are absorbed poorly, and long-standing deficiency of nutrients such as iron and zinc affects hair growth. That is covered properly in our guide to fat malabsorption symptoms. The second is shared metabolic ground: insulin resistance drives liver fat and also lowers sex hormone binding globulin, which raises free androgen levels, which matters for pattern hair loss. We set that mechanism out in how the liver and hormone balance really interact.
There is also the practical overlap that brings people here in the first place: rapid weight loss improves liver tests and simultaneously triggers telogen effluvium, so people often see their bloods improve and their hair shed in the same season. Both settle, at different speeds.
What we are not selling you here. Watermans makes hair and skin products. None of them affects your liver, your bile or any blood test on this page, so there is no product card. If your hair is shedding after weight loss or illness, a gentle sulphate-free shampoo reduces breakage while it recovers, and that is the entire claim.
Where to read next in this series
- Fatty liver diet: what actually reduces liver fat
- Fatty liver symptoms, and what shoulder pain really means
- Gallstones symptoms and when the pain is urgent
- Fat malabsorption: what pale stools, bloating and nausea can mean
- Liver and hormone balance: how SHBG really works
Frequently asked questions
Is a slightly raised ALT serious?
Usually not on its own, but it should never simply be ignored. The standard approach is to repeat it, review alcohol, weight and medication, check for hepatitis and other causes, and calculate a fibrosis score such as FIB-4 to work out whether scarring is likely. Persistent or rising results need proper follow-up.
Can I fast before a liver function test?
Fasting is not usually required for liver tests alone, though it often is if cholesterol or glucose are being measured at the same time. Prolonged fasting can slightly raise bilirubin, particularly in people with Gilbert's syndrome, so follow the instructions you are given.
Does exercise affect liver blood test results?
Yes. Strenuous exercise in the days before a test can raise AST and sometimes ALT, because both enzymes are present in muscle. If you train hard, mention it, because it is a common reason for an unexplained result that then normalises on a repeat.
What is a normal GGT level?
Reference ranges differ between laboratories and by sex, so read your result against the range printed on your own report rather than a figure from the internet. A raised GGT alone is very common and is interpreted alongside ALP, ALT, weight, alcohol and medication.
Can drinking more water improve my liver test?
No. Hydration matters for general health but it does not flush toxins or change liver enzymes. The measures that shift these numbers are weight, alcohol, activity and removing a medication or supplement that is causing the problem.
How long does it take for liver enzymes to come down?
It depends entirely on the cause. Enzymes raised by a medication often normalise within weeks of stopping it. Alcohol-related GGT often falls over 4 to 8 weeks of abstinence. Enzymes raised by fat in the liver follow weight and activity over months.
Is Gilbert's syndrome something to worry about?
No. It is a common, harmless inherited variation in how bilirubin is processed, affecting a few percent of people. Bilirubin rises during fasting, illness or stress and the eyes may look slightly yellow, but the liver is otherwise normal and no treatment is needed.
Should I get a private liver screen?
If you have symptoms or risk factors, going through your GP is usually better, because abnormal results need interpretation and follow-up rather than just a number. Private panels frequently produce mildly abnormal findings that then need NHS investigation anyway.
This article is general health information, not medical advice, and it cannot interpret your individual results. Discuss any abnormal blood test with your GP. Never stop or change a prescribed medicine, including a statin, without speaking to a healthcare professional.
